Version 2.8 is released under the NCSA/University of Illinois Open Source License.
The current version of DeTeX is detex-2.8.tar. The only change between detex 2.7 and 2.8 is the addition of the NCSA/University of Illinois Open Source License.
This patch has been incorporated into detex 2.7, so it is no longer necessary. However, if you are using flex, you'll probably need to change the link line in the make file to be
${CC} ${CFLAGS} -o $@ ${D_OBJ} -lfl
DeTeX is a filter program that removes the LaTeX (or TeX) control sequences from the input so that the real content can be passed to a spell or diction checker. I don't know of any use of dates anywhere in the program, so I think it should be Y2K compliant. However, I only distribute it in source form so you are advised to review the source and make sure it is suitable for your needs.
Detex is now available under the NCSA/University of Illinois Open Source License